Eighteen major species and five minor species of human interferon (IFN) alpha derived from Sendai virus induced human lymphoblastoid cells (Wellcom Research Laboratories) were isolated by monoclonal antibody affinity column chromatography and reverse phase high performance liquid chromatography (HPLC). The antiviral specific activity of the species varied on human fibroblast (HFS)(0.2-2.lE8 u/mg), bovine (MDBK) (1.3-2.6E8 u/mg, murine (L929) (I.OE4-7.2E5 u/mg) and human amniotic (WISH) (0.3-2.4E8 u/mg) cell lines. The apparent molecular weights of IFN alpha species ranged from 17,500 to 23,300 by SDS PAGE under non-reducing conditions. At least 9 species appear to be glyproteins based on the presence of amino sugars as determined by carbohydrate analysis. Preliminary studies have suggested that, in some species, the carbohydrate is linked to the amido nitrogen of asparagine which is evidenced by the presence of glucosamine. In some, the carbohydrate is linked to the hydroxyl oxygen of serine or threonine which is evidenced by the presence of galactosamine. Digestion of some species with neuraminidase and glycosidases have shown the presence of or absence of O-linked glycosylation using SDS PAGE as an indicator. Amino terminal amino acid sequence data on the species indicates that the amino termini ar similar; however, distinct differences were observed at several positions among the species. Several immunomodulatory activities of the IFN species were examined, including the inhibition of HIV and antiproliferative activity of U937 and Daudi cells; thus, IFN-alpha species exhibited antiproliferative and anti-HIV activities which differ among themselves.